Propulsion unit



Patented Dec; 15, 1936 I OFFICE PROPULSION UNIT PeterDe Michelis, Application June 10,

6' Claims. My invention relates to a propulsion unit, and

more particularly to improvements in screw propellers.

The broad object of my invention is to provide a propulsion unit which yields a. greater driving thrust at the available horse power.

A more specific object of my invention is t increase the efficiency of screw propellers.

A further object of my invention is to provide an improved combination rudder and propeller unit for small marine craft, such as speed boats. The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of my invention. It is to be understood that I do not limit myself to this disclosure of species of myinvention, as I may adopt va-' riant embodiments thereof within the scope of the claims.

Referring to the drawing:

Figure 1- is a. sideview, partly in section and partly in elevation, of the propulsion unit em- Figure 4 is a vertical sectional view of the prot peller blades, taken ina plane transversely through the mid-portion .of theblades when the latter are in alignment as illustrated in Fig. 3. In terms of broad inclusion, the propulsion unit embodying my invention comprises a plurality of axially aligned right and left-hand screw propellers in which the blades of a trailing propeller are pitched on both sides, and means for rotating the propellers in opposite directions. The oppositely rotating right and left-hand propellers mutually cooperate to increase the driving thrust by resolving rotational flow in the projected stream of fluid into useful sternward or axial fiow; this being effected by the tendency on the part of the trailing propeller to set up a spiral flow opposing that set up by the leading propeller. This beneficial effect of a second propeller is secured in the propulsion unit of my invention without materially increasleading propeller. As the fluid is projected rearwardly by the leading propeller it impinges on 55 the back sides of the blades on the trailing pro- San Francisco, Calif. 1933, Serial No. 675,234

peller, which sides are pitched so thata portion of the force of the impinging fluid is utilized to drive the propeller.

For purposes of detailed description, the propulsion unit of my invention is shown as embodied in a marine propeller construction; it being understood that this showing is merely for purposes of illustration, and 'that'the principles embodied in my invention apply equally well to propellers working in a medium of air, such as air craft propellers. The propulsion unit for small marine craft which has been chosen for purposes of illustration comprises a bracket 2 adapted for mountingon the rear end of a boat 3. and having a pair of vertically 6. The bracket .2 provides a pivotal mountin for a sectional housing preferably comprising an upper portion 1, an intermediate portion 8' and a lower portion 9 connected together by suitable bolts ll.

The intermediate section 8 of thehousing is provided with a pair of forwardly extending arms l2 carrying a pivot pin l3 journaled in the bracket portion 6 in suitable bearings l4. The upper portion 1 of the housing is provided with an-upwardly and forwardly extending bifurcated arm l6 carrying a pivot pin ll journaled in the upper bracket journal 4 in a suitable bearing I8. But one branch of the arm I6 is shown, the other being cutout of the view by. the plane of section.

The lower section or portion 9 of the housing is provided with suitable fins l9, so that the housing in effect provides a rudder with which. the boat 3 may be steered. Steering control for the rudder is provided by a laterally extending arm 2| secured to the upper pivot pin l1 and to which the steering cable 22 is fastened. Of course it is understood that another arm similar to the arm 2| but extending in the opposite direction is provided, to which another steering cable is connected; the latter arm and cable not being shown because of the sectional view. By this arrangement the rudder may beturned from side to side about its pivot axis by a steering wheel conveniently arranged adjacent the forward end of the boat, as will be readily understood.

A drive shaft 23, connecting with a suitable motor mounted in the boat, is journaled adja- I 15 spaced and rearwardly extending journals 4 and in suitable bearings 21. The shafts 23 and 26 are coupled by a universal joint 23 positioned intermediate and co-axial with the pivot pins 13 and ll of the rudder mounting. By'this arrangement the shaft 26 may be continuously driven by the shaft 23 and without interfering with the free pivotal movement of the rudder.

A vertical shaft 29 is provided, extending longitudinally of the housing, and is connected at its upper end with the driven shaft 26 by a pair of beveled gears 3|; these gears being enclosed by the upper portion 1 'of the housing. The vertical shaft 29 isjournaled in the housing in suitable bearings '32, and preferably comprises two sections coupled by a sleeve 33 so that the lower portion 9 of the rudder construction may be assembled as a unit.

The lower section 9 of the housing has an enlarged torpedo-shaped portion 34 which is split along a horizontal plane and held together by suitable screws 36 'to give access to the interior of this portion of the housing. A transversely extending sleeve 31 is journaled in this portion of the housing section 3 in suitable bearings 38; an end plate 39 being provided to hold the outer bearing in position. The sleeve 31 projects rearwardly from the housing, and carries on its projected end a screw propeller 4| held in place on the sleeve by a threaded collar 42. The propeller 4| is further held against axial movement by a set screw 43 and also by a flange 44 provided on the hub of the propeller and locked between the end of the sleeve 31 and the retaining collar 42.

A propeller shaft 46 is journaled in the sleeve 31 in suitable bearings 41, and is also joumaled adjacent its forward end in the housing in a suitable bearing 48. This shaft projects rearwardly beyond the sleeve 31, and carries on its projecting end a second propeller 49. The latter propeller is held fixed on the shaft by a set screw 5| and also by a nut 52 threaded on the end of the shaft.

The sleeve '31 and propeller shaft'46 each carry adjacent their forward .ends a beveled gear 53 meshed with a beveled pinion 54 flxed on the lower end of the vertical or longitudinally extending shaft 29. By this arrangement rotation of the drive shaft 23 will effect rotation of the propellers 4| and 49, but in opposite directions. The beveled gears 53 are preferably of the same size, so that the propellers are rotated at substantially the same speed.

As best shown in Figure 3, one of the axially aligned propellers is a right-hand screw propeller and the other is a left-hand screw propeller. The blades of these propellers are preferably of substantially equal size, and preferably have driving faces of substantially equal pitch. This pitch may be either straight or expending. I have used a 17 inch straight pitch with good results.

An important feature of my invention is the pitching of the back sides of the trailing propeller blades. The leading propeller 4| is of ordinary propeller design with blades having pitched driving faces providing a concave surface as shown in Fig. 4, but the trailing propeller 49 has blades which are pitched on both the front and back sides. The back sides of the trailing propeller (the sides facing theleading propeller) are concave as shown in Figure 4, and have a pitch which is preferably less than the pitch of the front or driving sides of the blades. 1 have used a 15 inch straight pitch with good results. Of course the pitching of the back side of the blade forms a surface which is reversely curved relative to the front surface of the blade. In order to take care of this the trailing edge of the blade is made somewhat heavier; or thicker than the leading edge. Figure 4 brings out these features of construction.

As shown in Figure 1, the hubs of the adjacently'positioned propellers are shaped and proportioned so that together they form a bulletshaped body; this body maintaining the lines and providing. the trailing portions of the torpedo-shaped body 34 of the housing. This construction and design is important in the interest of minimizing resistance to passage through the water.

A feature of construction tobe noted is that the lower portion 9 of the mechanism, which comprises the driving head of my propulsion unit, is demountable and designed for attachment to the power unit of an ordinary outboard motor. my construction, as will be readily appreciated.

While numerous refinements are numbered among the improvements of my invention, it will be seen that the broad combination of elements comprises a plurality of axially aligned right and left-hand screw propellers in which the blades of a trailing propeller are pitched on both sides, and means for rotating the propellers in opposite directions. I have found that screw propellers operated in this manner mutually cooperate in their action in the water, which coaction yields a performance of new functions with the production of new and improved results as evidenced by an increased driving thrust at the available horse power.

The increased driving thrust afforded by the propulsion unit is attributable largely to the tendency on the part of the trailing propeller to reduce or eliminate rotation in the rearwardly moving column or stream, and to divert this rotational flow into useful sternward flow.

It is well known that the driving thrust of a screw propeller is derived from its projecting a mass of fluid through the surrounding fluid medium. The reactionary force of the propeller in projecting this mass of fluid constitutes the driving thrust, and is directly proportional propulsion unit of my invention the trailing propeller tends to set up a spiral rotating in a direction opposite to that of the leading propeller. Since the propellersare of substantially equal size and pitch and rotate at substantially the same speed, the two superimposed spirals tend to neutralize each other and the rotational flow is resolved into axial flow. This increases the sternward velocity of the projected column of fluid, with a consequent increase in the drivin'g thrust of the propellers.

Not only is the loss due to rotational slip largely eliminated, but. it is thought that the This adaptability increases the utility of I The rotational effect serves no useful pur- I pose and may be called wasteful, slip. In thecoacting propellers function to reduce losses due peller, and losses due to cavitation at the latter propeller are decreased.

This desirable twin propeller action is secured 10. by the propulsion unit of my invention without materially increasing the power required to drive the unit over that required to drive a single propeller. As the fluid is projected rearwardly by the leading propeller it impinges on the back sides of the blades on the trailing propeller, which sides are pitched so that a portion of the force ofthe impinging fluid is "utilized to drive the propeller. In the two blade propeller unit shown for purposes of illustration there will be times during the revolution when the trailing propeller receives more turning thrust than others; viz., those times when the blades of the two propellers are opposed. In other words, the driving will be by impulses. By increasing the number of blades on one or both propellers the impulses will be brought closer together and approach a constantly applied turning force. I have used a three blade trailing propeller in combination with a two blade leading propeller withgood results.

I claim:

1. A propulsion unit comprising a plurality of axially aligned right and left-hand screw propellers, the back sides of the blades on a trailing propeller being concave and pitched so that fluid projected from a leading propeller and impinging thereonaids said trailing propeller in its-rotation, and means for rotating the propellers in opposite direction.

2. A propulsion unit comprising a plurality of axiallyzaligned right and left-hand screw propellers, the drivingfaces of said propellers being curved and the back faces of a trailing propeller being reversely curved relative to said driving faces, and means for rotating the propellers in opposite directions.

'3. A propulsion unit comprising a plurality of axially aligned right and left-hand screw propellers, the driving faces of a leading propeller and both the driving and back faces of a trailing propeller being concave, and means for rotatin'g the propellers in opposite directions.

4. A propulsion unit comprising a plurality of axially aligned right and left-hand screw propellers, the driving faces of a leading propeller and both the driving and back faces of a trailing propeller being concave, the trailing edges of blades of the trailing propeller being thicker than the leading edges, and means for rotating the propellers in opposite directions. V 5. A propulsion unit comprising a split housing, a shaft arranged in and projecting from the housing, a sleeve encircling the shaft and.

also projecting from the housing, propellers on the outer projecting ends of said shaft and sleeve, driving gears on the inner ends of the shaft and sleeve, bearings for journalling the sleeve and held between the sections of said housing, and a bearing for journalling the inner rings in the sleeve for Journalling the shaft.

PETER DE MICHELIS. 

